Iraq is increasingly turning to other governments like Iran, Russia and Syria to help beat back a rampant insurgency because it cannot wait for additional American military aid, Baghdad's top envoy to the US says.

Such alliances test the Obama administration's influence overseas and raise risks for the US as some of its main global opponents consider joining forces. Moreover, a partnership that stretches from Tehran and through Baghdad into Damascus could also solidify a Shiite-led crescent across much of the Mideast at a time when the Sunni-led insurgency in Iraq is trying to create an Islamic state through the region.

Iraqi Ambassador Lukman Faily stopped short of describing enduring military relationships with any of the other nations that are offering to help Iraq fight the Islamic State of Iraq and Syria (Isis). And he said Baghdad would prefer to work with the US.

But Faily said delays in US aid have forced Iraq to seek help elsewhere. He also called on the US to launch targeted airstrikes as a "crucial" step against the insurgency. So far, the Obama administration has resisted airstrikes in Iraq but has not ruled them out.

"Time is not on our side," Faily told an audience at the Carnegie Endowment for International Peace in Washington. "Further delay only benefits the terrorists."

His comments came as chaos in Baghdad continued.

Despite a constitutional deadline to name a new parliament speaker, minority Sunni and Kurdish lawmakers walked out of the first session of the newly seated legislature on Tuesday (local time), dashing hopes for the quick formation of a new government that could hold the country together in the face of a militant blitz. Hours later, Isis leader Abu Bakr al-Baghdadi called on Muslims worldwide to join the battle and help build an Islamic state in land that the extremist group controls in Iraq and Syria.

Meanwhile, the United Nations said more than 2400 people were killed in Iraq in June, making it the deadliest month in the country in years.

The Obama administration has been hesitant to send much military aid to Iraq for fear of dragging the US into another years-long Mideast war. President Barack Obama has ruled out sending combat troops back into Iraq after withdrawing US forces in 2011, but this week sent more soldiers to Baghdad to help bolster the US Embassy. All told, officials said, there are about 750 US troops in Iraq - about half of which are advising Iraqi counterterror forces fight Isis.

At the peak of the eight-year war, more than 160,000 US troops were fighting in Iraq.

Since then, Washington has sold more than US$10 billion in military equipment and weapons to Baghdad, and recently stepped up its surveillance and intelligence support to its security forces.

The Pentagon's press secretary, Navy Rear Admiral John Kirby, said on Tuesday that the insurgent threat to Baghdad "is still very legitimate", and the military situation is fluid as Iraqi security forces try to hold their ground.

"It's a contested environment right now," Kirby said.

The additional 300 US troops moving into Iraq this week were equipped with an unspecified number of army Apache attack helicopters as well as unarmed surveillance drones, Kirby said. The total 750 troops includes about 100 who were there before the Islamic insurgents' offensive.

Iraq has been pleading with Washington more than a year for additional help, and Faily said the worsening battle with Isis has forced leaders in Baghdad to take whatever aid is available most quickly.

"That choice is primarily from the need, rather than the desire," Faily said.

Noting international bans on Iranian military sales, Faily said Iraq is mostly seeking Tehran's advice on how to combat Isis - a foe that Iran has faced in Syria's civil war. Isis is one of a number of Sunni-led groups that have been fighting for three years to force President Bashar Assad from power.

Assad is an Alawite, a religious sect that is an offshoot of Shiite Islam, and Iraqi Prime Minister Nouri al-Maliki is Shiite. Faily said Baghdad would be willing to work with the Syrian government to control the border between the two nations, and keep it from falling into Isis's hands.

And he said Russia's fighter jets and pilots have been willing to fill Iraq's air support needs.

Plans to send US fighter jets to Iraq have been stalled, although State Department deputy spokeswoman Marie Harf said some F-16s could be delivered this autumn.